1. Field of the Invention
The present invention relates to an electron microscope equipped with a magnetic microprobe.
2. Description of Related Art
In the prior art, in a transmission electron microscope, a specimen has been observed by directing an electron beam at the specimen such that the beam is transmitted through the specimen to create a specimen image, magnifying the specimen image by a magnetic lens, and projecting the image onto a screen. A technique for inserting a biprism into such a conventional transmission electron microscope is known as described, for example, in Japanese Patent Laid-Open No. 2002-117800 (pages 3 and 4; FIG. 1). The biprism creates interference fringes (hologram) by interference between the electron beam passing through a vacuum and the beam transmitted through the specimen. Information about variations in the phase of the beam is taken from the hologram. Information about the thickness distribution across the specimen, the electric field, or the magnetic field is obtained.
Furthermore, a technique utilizing a mechanism for removing contamination from a wire forming such a biprism is known (see, for example, Japanese Patent Laid-Open No. H9-80199 (pages 2, 3, and 4; FIG. 2)).
In a further known technique, a magnetic field application means is installed between the polepieces of the objective lens of an electron microscope. A DC current produced by a magnetic field application power supply or an AC current having an arbitrary phase, period, or amplitude is applied to the magnetic field application means with an arbitrary synchronizing signal to obtain information about magnetic domain structure while observing an electron microscope image of a magnetic material to which a magnetic field is applied (see, for example, Japanese Patent Laid-Open No. H8-96737 (pages 2 and 3; FIG. 1)).
In the prior art electron microscope, an external magnetic field is applied to a magnetic material to induce variations in the magnetic field inside and near the specimen. The induced variations are observed by application of a magnetic field. The following methods are available to apply this magnetic field.
1. The magnetic field produced by the objective lens of the electron microscope is used as the field applied to the specimen.
2. A coil used only for the application of the magnetic field is mounted either in the specimen chamber of the microscope or in a specimen holder.
FIG. 8 illustrates the prior art method of applying a magnetic field to a specimen. The specimen, indicated by numeral 1, is made of a magnetic material and held by a specimen holder 2. An excitation coil 3 is used to apply a magnetic field to the specimen 1. Indicated by e is an electron beam. Magnetic flux going out of the N pole of the excitation coil 3 enters the exciting coil 3 on the S-pole side. At this time, the magnetic flux 4 produced by the excitation coil 3 for producing a magnetic field penetrates through the specimen 1 of magnetic material, thus applying a magnetic field to the specimen 1. The beam e is directed at the specimen 1.
In the above-described prior art method, the magnetic field produced by the excitation coil is applied to the specimen of magnetic material. With this method, a substantially uniform magnetic field is applied to the whole specimen. However, if the applied magnetic field is strong (e.g., more than hundreds of gauss), the incident electron beam is deflected to a great extent by the magnetic field because the uniform magnetic field is applied over a wide range and over the whole specimen in this way. That is, with the prior art method described above, a strong magnetic field cannot be applied to the specimen of magnetic material. Consequently, imaging under environments of such strong magnetic fields cannot be performed.